Rapid growth of garnet within a metamorphic vein inferred from misorientation angle distribution of garnet porphyroblasts

Atsushi Okamoto, Katsuyoshi Michibayashi

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The microstructure of garnet aggregates within a metamorphic vein are investigated to constrain the duration of vein formation. Garnet-bearing veins occur subparallel to the foliation of a host mafic schist in the Sanbagawa metamorphic belt, Japan. Microstructural observations using SEM, EPMA and EBSD reveal that numerous small garnets (10-100 μm diameter) coalesced to form large porphyroblasts within the vein. EBSD analysis of the porphyroblasts reveals that misorientation angles of neighbor-pair garnet grains within the vein have a random distribution. This contrasts with previous studies that found coalescence of garnets in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation-driven rotation. The random misorientation angle distribution indicates that (1) garnets within the vein grew so fast that they could not rotate within the vein, and thus (2) random orientations of garnets at the nucleation stage were preserved. On the basis of a simple kinetic model that assumes rotation of garnet is rate-limited by diffusion creep of matrix quartz, the time taken for a small garnet grain to rotate 1° is estimated to be 10 3 - 10 4 years. This duration may indicate the upper limit of the duration of garnet growth, and of vein formation.

Original languageEnglish
Title of host publicationWATER DYNAMICS
Subtitle of host publication3rd International Workshop on Water Dynamics
Pages167-170
Number of pages4
DOIs
Publication statusPublished - 2006 May 15
EventWATER DYANMICS: 3rd International Workshop on Water Dynamics - Sendai, Japan
Duration: 2005 Nov 162005 Nov 17

Publication series

NameAIP Conference Proceedings
Volume833
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616

Other

OtherWATER DYANMICS: 3rd International Workshop on Water Dynamics
CountryJapan
CitySendai
Period05/11/1605/11/17

Keywords

  • Garnet aggregate
  • Misorientation
  • Sanbagawa metamorphic belt
  • Vein

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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    Okamoto, A., & Michibayashi, K. (2006). Rapid growth of garnet within a metamorphic vein inferred from misorientation angle distribution of garnet porphyroblasts. In WATER DYNAMICS: 3rd International Workshop on Water Dynamics (pp. 167-170). (AIP Conference Proceedings; Vol. 833). https://doi.org/10.1063/1.2207097